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Discuss the various roles that lipids play in living organisms.

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Discuss the various roles that lipids play in living organisms. Lipids contain O, C and H, and they play very crucial roles within living organisms. Lipids are non-polar and have little or no affinity for water. It is made by joining 2 different types of molecules by esterification, a condensation reaction. Some of the important lipids are: 1. phospholipids 2. triglycerides 3. steroids such as cholesterol 4. complex lipids such as glycolipids and lipoproteins 5. sphingolipids 6. waxes Phospholipids consist of a phosphate head and a hydrocarbon tail. This results in the phosphate head being hydrophilic and the hydrocarbon tail being hydrophilic. This amphipathic nature of the phospholipid molecule is especially important in forming the phospholipid bilayer of the cell membrane. The hydrophilic regions face the exterior and interior off the cell whereas the hydrophobic hydrocarbon tails associate together to form the interior of the cell membrane. This cell membrane is impermeable to ions and charged molecules, no matter how small the size. This is especially important in the formation of ATP, the energy currency of the cell. Because the inner membrane of the mitochondrion is impermeable to protons, the protons will have to diffuse back to the matrix via ATP synthase, and hence ATP is synthesized. If the membrane is leaky to protons, there will be no electrochemical gradient, and hence no proton motive force. ...read more.


Each molecule of glycerol forms as many ATPs as half a molecule of glucose. Triglycerides are stored just beneath the skin in adipose tissues and also surrounding the organs. Subcutaneous fats serve as heat insulators for animals living in cold climates, as lipid are poor conductors of heat. This is especially important for animals living in the Artic climate like the polar bears. Fats in adipose tissues surrounding vital organs such as the heart, eyes, and kidneys, serve to protect the organs from damages. On oxidation of triglycerides, water is formed as a by-product. Desert animals such as the kangaroo rat stores fat as a source of water. Cholesterol is an important class of lipids for maintaining membrane fluidity. It spans only one layer of the phospholipid bilayer and is absent from the inner membranes of the chloroplast and the mitochondria. A cholesterol molecule is hydrogen-bonded to a phospholipid molecule in the cell membrane. Cholesterol has the dual effect of increasing membrane fluidity at low temperature, and decreasing it at high temperatures. The intercalation of cholesterol molecules into the lipid monolayers results in reduced membrane fluidity at high temperatures as cholesterol prevents close-packing of the phospholipid molecules. At lower temperatures, cholesterol prevents the hydrocarbon chains of the phospholipids from aggregating as temperature is decreased, thereby reducing the tendency of membranes to freeze upon cooling. Apart from maintaining membrane fluidity, cholesterol decreases the permeability of a lipid bilayer to ions and small polar molecules by filling in the spaces between hydrocarbon chains of membrane phospholipids. ...read more.


Cell recognition ensures that the antibodies in out body will attach foreign bacteria and germs and not our own cells. It also prevents auto-immune disease where the immune system destroys our own cells. Glycolipids also contribute to membrane stability, because as they are highly hydrophilic, the sugars help to orientate the glycolipids in the membrane so that they are kept in contact with the external aqueous environment and are unlikely to rotate towards the interior or diffuse transversely. The sphingolipids, like the phospholipids, are composed of a polar head group and two nonpolar tails. The core of sphingolipids is the long-chain amino alcohol, sphingosine. The sphingolipids include sphingomyelins and glycosphingolipids. Sphingomyelins are the only sphingolipid that are also phospholipids. Sphingolipids are a component of all membranes but are particularly abundant in the myelin sheath. Waxes are similar to fats and oils but their long-chained fatty acids are linked to a long-chained alcohol. Hence, it is totally insoluble in water and is chemically inert. In plants, it forms a waxy cuticle that covers the epidermis of the leaves and stems to prevent excessive loss of water through evaporation and cuticular transpiration. It limits the diffusion of water into the plant that could affect the water potential of the leaf, and it protects the leaf from parasites to a certain extent. In insects, they also have a layer of waxy cuticle to help cut down on water loss. Bee wax is an abdominal secretion of bees and they use it to hive their cells. ...read more.

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